The present invention relates to a method and apparatus for the variable control of a valve of an internal combustion engine, especially for the throttle free load control of an Otto carburetor or reciprocating engine via the lifting or stroke function of one or more intake valves per cylinder.
The advantages of a variable valve control for internal combustion engines have been known for a long time. By variably controlling the charge valves the torque curve can be improved or the maximum power can be increased. Also, the raw emissions can be decreased or the losses of charges can be significantly reduced, if the charge and/or load control takes place without using a throttle valve but only by the variation of the lift or opening duration of the inlet or intake valves. Correspondingly there are numerous suggestions in the literature for a variable valve control of internal combustion engines.
In the generic BE-PS 885.719 an opening camshaft and a closing camshaft cooperate with a rocker arm which is supported on the valve stem of an intake valve. In order for the rocker arm to maintain a defined position when the intake valve is closed a spring is provided which continuously presses the rocker arm against the cams of both camshafts. Thereby the rocker arm temporarily withdraws from the valve stem. This renders the application of an automatic valve clearance compensation considerably difficult. Furthermore, both camshafts are permanently in a friction contact with the valve rocker which increases the friction losses of the valve drive.
DE 35 31 000 A1 describes a device for the decrease of throttle losses with piston engines under partial load by means of phase control of the valves whereby a rocker lever is supported on a valve stem and its two ends cooperate with a respective camshaft. A characteristic of this cam drive is that each time only half the lift of a cam can be taken advantage of and the opening and closing movements of the valves are determined by the contours of the two cams by means of which unacceptably high accelerations may occur.
A further suggestion for a variable valve control for a lifting cylinders combustion engine can be found in DE 35 19 319 A1. With this variable valve control an intake valve can be actuated by a rotating lift camshaft by means of a valve lever which can be pivotable about a slidable bearing against the force of a valve spring. A control camshaft that rotates at the same speed as the lift camshaft additionally engages the valve lever and controls the pivoting movement of the lever as a function of operating parameters of the internal combustion engine. A characteristic of this known valve control is that the valve opening or closing movement, as a result of the phase relationship of the lift camshaft and the control camshaft, is determined by the cam contours of both camshafts, by which unacceptably high valve accelerations or speeds can occur on closing when placing the valve into its position, or the maximum rate of revolutions of the combustion engine is unacceptably restricted.
A further device for a variable valve control is described in U.S. Pat. No. 5,178,105. This reference deals with the problem of adjusting the control timings of the valves to different rates of revolutions. For this purpose the device comprises two camshafts, the cams of which are formed mirror-inverted towards each other and respectively pass from a point of minimal lobe via a steep section and a flat section into a point of maximum lobe. The two cams act on a common feeler-element or follower which in cross section is triangular and is pivotably guided directly on a stem of the valve that is to be actuated. The opening and closing phase of the valve is respectively determined by the addition of the lift functions which both cams carry out in respect to the follower, by means of which as a result of the phase relationship of the camshafts the valve movement is alterable in certain limits. As to the design of the cams there are distinct restrictions since in certain phases the follower is shifted by the two cams only relative to the stem without a resulting lift movement of the valve. Furthermore, the closing position of the follower is a result of the phase relationship of the camshafts which requires a very sophisticated valve adjusting device which, at rapid phase changes, can lead to problems in the valve drive.
The object of the invention is to create a method for the variable control of a valve of an internal combustion engine, in particular for the throttlefree load control of an Otto carburetor engine via the lift function of one or several intake valves per cylinder, which at high operating reliability unites a cost-efficient manufacturing with the possibility of providing an automatic valve clearance compensation. A further object of the invention is to provide a device for the performance of this method.